Ionomeric coatings

ABSTRACT

Heat cured, thermoset protective surface coating films applied to a substrate are produced preferably by a dual cure of a polymeric ionomeric binder comprising zinc modified carboxyl functional epoxy-ester polymers. The epoxy-ester polymer contains both carboxy and hydroxyl functionality and coreacts with a zinc salt selected from a zinc carbonate or an organic zinc salt having a pKa above about 3.0. Upon heat curing, the carboxyl and hydroxyl groups crosslink while the zinc forms a zinc cluster to produce a thermoset film.

This is a continuation of Ser. No. 397,278, filed Aug. 23, 1989, nowU.S. Pat. No. 5,025,063.

BACKGROUND OF THE INVENTION

Protective or surface coatings are organic compositions applied tosubstrates to form continuous films which are cured or otherwisehardened to provide protection as well as a decorative appearance to thesubstrate. Protective surface coatings ordinarily comprise an organicpolymeric binder, pigments, inert fillers and other additives. Thepolymeric binder functions as a dispersant for the pigments, inerts, andother additives in wet coating compositions and further functions as abinder for the pigments and inert fillers in the cured or hardened paintfilm. Polymeric binders can be thermoplastic or thermosetting bindersbased on coreactive components such as a reactive functional polymeradapted to crosslink or coreact with a crosslinking component such asmelamine, isocyanate, or epoxy.

Conventional thermosetting polymers often require high temperatures aswell as external crosslinkers. Some crosslinkers, such as melamines inconventional industrial coatings or triglyoidyl isocyanurate for powdercoatings, can cause toxicity problems. Also, the release of volatileby-products, such as aprolactam, from some of these materials can causefilm defects, such as cratering and bubbling.

It now has been found that excellent paint coatings can be producedbased on a dual cure of esterifiable ionomeric polymeric bindercomprising a carbolic acid functional polymer of an epoxy-ester polymerwhich is at least partially neutralized with an organic zinc salt suchas zinc acetate, zinc propionate, or a similar organic zinc salt, or thezinc inorganic salt of zinc carbonate to form an ionomer. In addition toionomer formation, epoxy-esters can self-cure through an esterificationreaction between excess carboxyl groups and hydroxyl groups on the epoxybackbone.

The epoxy-ester polymer was found to provide interreacting polymerchains which exhibit thermosetting properties comparable to coreactivepolymeric binders crosslinked by an amino crosslinker. An ionomer can bedefined as a polymer composed of a polymeric backbone containing a smallamount of pendant carboxylic acid groups, usually less than 15 moleportent, which are neutralized partially or completely with an organiczinc salt or zinc carbonate to form an ionomer. These ionic moieties andtheir interactions dominate the behavior of the polymer itself where itis believed that the zinc ions are exchanged for a hydrogen ion of thepolymer carboxyl group. Ionic hydrocarbon polymers for elastomers orplastics are disclosed in U.S. Pat. No. 3,264,272.

In accordance with this invention, changes in the properties ofpolymeric binders for paint coatings can be achieved through theintroduction of zinc metal ions by way of an organic zinc salt or zinccarbonate where modification of polymer properties is believed due toaggregation of ions. For example, the correction of two ion pairs onadjacent polymer chains results in a four-centered aggregate whichbehaves essentially like a crosslink. Among the dramatic effects thathave been observed with paint compositions are increases in the moduli,increases in glass transition temperatures, and increases inviscosities. The formation of ionomeric clusters in protective surfacecoatings causes the acid functional polymers to behave like aphase-separated block copolymer. The use of ionomers in powder coatingsis particularly advantageous since it permits control of the processsuch that the temperature during extrusion is lower than that of thevolatilization temperature of the counterion (in the acid form). Thus,the ionomeric crosslinks are not formed to a significant extent duringprocessing of the coating or application to a substrate, or during flowout and leveling to form a smooth continuous film. In this invention,the majority of the ionomer formation takes place during the bake cyclewhich comprises temperatures higher than the temperature where the saltwill melt or solubilize and participate in an equilibrium reaction ofthe acid functional polymer. Baking and curing conditions can becontrolled so that the ionomer formation occurs during baking wheretemperatures are adjusted to that of the volatilization temperature ofthe acidified counterion. The ionomeric formations can be observed inpowder coatings especially as well as solvent borne coatings such ashigh solids coatings.

The unique properties of ionomers offer an alternate curing mechanismfor solvent and high solids coatings generally, and powder coatingsespecially, with potential for lower baking temperatures, less filmsdefects, a unique balance of physical properties, less toxic pouringchemistry, thermal reversibility and lower cost. Thus, the addition oflow levels of ionic zinc groups to avoid functional epoxy-esterpolymeric binders has been found to have dramatic effects on thephysical properties of the polymeric binder. Incorporation of zincorganic salts or zinc carbonate, for instance, causes an epoxy-esterpolymer to exhibit improved film properties such as solvent resistanceand hardness. Viscometry has also supported the formation of ionomericdomains in carboxylic acid functional systems, but with ioniccrosslinking, these properties are known to be thermally reversible.Useful carboxyl epoxy-ester polymers characteristically exhibit lowpolarity, high hydrophobicity, and low hydrogen bonding characteristics.Zinc ionomers generally resist water or humidity and produce coatingswhich are not water sensitive. In addition to ionic crosslinking, thecarboxyl functional epoxy-esters have the capacity to self-cure throughan esterification reaction cure. The excess carboxyl groups in theepoxy-ester react under normal curing conditions with hydroxyl groups onthe backbone of the epoxy moiety to form ester crosslinks. Thisesterification cure can produce good paint properties by itself, butsuperior properties can be obtained by including a zinc salt, such thata dual-cure is produced The dual ionomeric-esterification cure producesfilms with superior hardness, flexibility, solvent resistance andweathering resistance. Good weathering resistance is not commonlyobtained with paints containing large quantities of epoxy and,consequently, good weathering was surprising and unanticipated.

When zinc carbonate is used as the neutralizing salt, the esterificationand ionomer cure produces water and carbon dioxide as by-products, sothe ionomeric-ester is a low toxicity cure mechanism. In addition,various quantities of zinc salt can be added to achieve a balance ofproperties so this dual-cure system provides the paint formulator with awide paint formulating latitude. These and other advantages of thisinvention will become more apparent by referring to the detaileddescription and illustrative examples.

SUMMARY OF THE INVENTION

Briefly, the coating composition of this invention is based on apolymeric binder comprising a carboxylic acid functional, epoxy-esterpolymer, which is at least partially neutralized with organic zinc saltor zinc carbonate to produce an ionomer. The polymer is adapted to geland provide esterification cure characteristics when heat cured as paintfilms, and can also provide ionomer characteristics if formulated as adual cure system. Preferred coating compositions comprise powdercoatings. Carboxylic acid functional epoxy-ester polymers containionizable carboxylic acid monomer sufficient to give an acid number ofat least 10. Superior properties are obtained with at least 10%neutralization of the carboxylic avoid by a zinc organic salt or zinccarbonate.

DETAILED DESCRIPTION OF THE INVENTION

The coating composition of this invention are based on a polymericbinder comprising a carboxylic acid functional epoxy-ester polymer whichis at least partially neutralized with an organic zinc salt or zinccarbonate.

In regard to the epoxy-ester polymers, it is believed that polarityand/or the hydrogen bonding capacity of the preferred epoxy-esterpolymers relates to their ability to form good ionomers Polymers withlow polarity and lower hydrogen bonding tendencies are generallyhydrophobic. Ionic groups generally present in a hydrophobic environmenthave a greater tendency to associate in clusters or multiplets, thusavoiding the unfavorable hydrophobic environment. Bisphenol A typeepoxies are sufficiently hydrophobic to produce good ionomers.

In accordance with a preferred embodiment of this invention, a carboxylfunctional polymer comprising an epoxy-ester polymer provides aparticularly useful ionomer. Upon pouring with a zinc organic salt orzinc carbonate, the epoxy-ester ionomer cures by ionomeric linking andester crosslinking to form hard films with excellent solvent, impact,and bend resistance along with other desirable film integrityproperties. Epoxy-esters provide cured films exhibiting an excellentblend and balance of film physical properties, particularly in respectto cured film hardness and flexiblity. Preferred coating compositionscomprise powder coatings which require lower molecular weight polymersto permit processing and compounding along with good flow and levelingof the powder coating during the film formation and heat curing step.For good storage stability, powder coatings should have tasktemperatures above 60° C. to avoid fusion. Thus, polymers useful inpowder coatings necessarily require a high Tg and/or crystallinecharacteristics. Ionic domains in high molecular weight polymers providetoughness along with reinforcing the polymer and improving the polymerhardness properties. It appears that the combination of low molecularweight but high Tg in conjunction with hard ionic domains from ioniccrosslinking can render ionomeric based powder coatings somewhatinflexible. However, the epoxy-ester ionomeric polymers in accordancewith this preferred aspect of the invention provide excellent powdercoatings where the cured films exhibit high hardness in combination withgood flexibility. The reactive epoxy-ester comprises an ester reactionproduct of an epoxide functional resin and a carboxylic acid. Forinstance, suitable epoxy-ester polymers can be produced by reacting amonofunctional or difunotional or higher functional epoxide resin with adifunctional or polyfunctional carbolic acid to produce a carboxylfunctional epoxy-ester copolymer, as hereinafter described.

Epoxide functional resins which can be reacted with such carboxylicacids are characterized by the three-membered ether group: ##STR1##where any one of the hydrogen can be a lower alkyl group, and where saidthree-membered ring is commonly referred to as an epoxy or oxiranegroup, where such groups typically terminate epoxy backbone chainsand/or branched chains. Epoxy-ester groups are formed by esterificationof an epoxy group with a carboxyl functional material to produce ahydroxy ester. Useful epoxide functional resin comprise conventionalepoxy resins, glyoidyl functional resins, and alkylene oxide resins.Epoxy resins are predominantly linear chain molecules comprising thecorrelation product of polynuclear dihydroxy phenols or bisphenols withhalohydrins to produce epoxy resins containing at least one andpreferably two epoxy groups per molecule. The most common bisphenols arebisphenol-A, bisphenol-F, bisphenol-S, and 4,4'- dihydroxy bisphenol,with the most preferred being bisphenol-A. Halohydrins includeepiphlorohydrin, diohlorohydrin, and 1,2-dichloro-3-hydroxypropane withthe most preferred being epiohlorohydrin. Preferred epoxy resinscomprise the coreaction product of excess molar equivalents ofepichlorohydrin with bisphenol-A to produce predominantly an epoxy groupterminated linear molecular chain of repeating units of diglycidyl etherof bisphenol-A containing between 2 and 25 repeating copolymerized unitsof diglycidyl ether of bisphenol-A. In practice, an excess molarequivalent of epichlorohydrin is reacted with bisphenol-A to produceepoxy resins where up to two moles of epiohlorohydrin coreact with onemole of bisphenol-A, although less than complete reaction can producedifunotional epoxy resin along with monoepoxide chains terminated at theother end with a bisphenol-A unit. The most preferred linear epoxyresins are polyglycidyl ethers of bisphenol-A having terminating1,2-epoxide groups and an epoxy equivalent weight between 140 and 5,000,and a number average molecular weight from about 280 to 10,000 asmeasured by gel permeation chromatography (GPC) as measured by ASTMmethods such as D3536-76, D3593-80, or D3016-78. Commercially availablelower molecular weight resins include Dow Chemical epoxy resinsidentified by trade number and average molecular weights as follows: DER333 (380); DER 66(525); while Shell Chemical epoxy resins are EPON 828(380); EPON 836 (625); EPON 100(525); EPON 1007 F (4000); and Ciba-Geigylinear epoxy resins GT-7013(1400); GT-7014 (1500); GT 7074 (2000); andGT-259 (1200). Although not as common, trifunctional epoxy resins areuseful comprising branched chain epoxy resins where the branched chainsas well as the backbone chain are each terminated with a terminalepoxide group to provide greater than two epoxide functionality.Trifunctional epoxy resins can be produced by overeating epiohlorohydrinwith polynuclear polyhydroxy phenols, trifunctional phenols, oraliphatic trifunctional alcohols.

Epoxy resins further include non-aqueous alkylene oxide resins which areepoxide functional resins comprising an alkylene oxide adduct of abisphenol compound. The alkylene oxide is an aliphatic alkyl derivativehaving up to about 26 carbon atoms although preferred oxides are loweralkyl oxides such as ethylene, propylene, and butylene oxides. Bisphenolcompounds include bisphenol-A, bisphenol-F and bissulfone or sulfides.Typically two or more moles of alkyl oxide are coreacted with one moleof bisphenol compound. Preferred compositions are 2:% molar reactions.Suitable molecular weight range of alkylene oxide resins is between 200and 1,000 as measured by GPC.

Epoxy resins further include non-aqueous hydroxyl functional glycidylacrylate or methaorylate copolymers with other ethylenically unsaturatedmonomers. Glycidyl monomers are oxirane functional monomers containingpendant ethylenic double bond unsaturation and includes, for example,acrylic, methacrylic, or vinyl derivatives of glycidol. Preferredoxirane monomers contain pendant oxirane and include glycidyl acrylate,glycidyl methacrylate, and allyl glycidyl ether. The oxirane monomerscan be copolymerized in the absence of water with other ethylenioallyunsaturated monomers which include, for example, vinyl aromatic andaliphatic hydrocarbons such as styrene, alpha-methyl styrene and similarsubstituted styrenes, vinyl naphthalene, vinyl toluene, divinyl benzene,and vinyl aliphatic hydrocarbons such 1,3 -butadiene,methyl-2-butadiene, 2,3-dimethyl butadiene, cyolopentadiene anddicyolopentadiene as well as ethylenically unsaturated esters and acidssuch as acrylic, methaorylic, ethaorylic, oinnamic and orotonio and thelike and esters containing fumaric and maleic type unsaturation.Particularly preferred monomers include, for example, styrene,alpha-methyl styrene, tertiary butyl styrene, divinyl benzene, 1,3-butadiene, isoprene, alkyl aorylates such as ethyl acrylate, butylaorylate, methyl-methacrylate, acrylonitrile, vinyl acrylate, and vinylmethacrylate as well as similar ethylenioally unsaturated monomers. Toprovide hydroxyl funotionality in the glyoidyl polymer, hydroxyfunctional ethylenically unsaturated monomers can be copolymerized suchas hydroxy alkyl acrylates or methaorylates. Preferred hydroxyl monomersare 2-hydroxy ethyl acrylate and methacrylate and 2-hydroxyl propylaorylate and methacrylate. The monomer mixture on a weight basis cancontain between 0.2% and 30% oxirane monomer, between 0% and 40%hydroxyl functional monomer, with the balance being other ethylenicallyunsaturated monomers.

The foregoing epoxy resin including alkylene oxide resins and glyoidylacrylate resins are coreacted with di or polyfunctional carboxylic acidcompounds in accordance with this invention to produce an epoxy resinwith both acid and hydroxyl functionality. Suitable linear dicarboxylicacids include oxalic acid, malonic acid, suocinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebaoic acid,dodecane dioarboxylio acid, and dimer fatty acids. Aromatic dicarboxylicand polybasic acids include phthalic acid and anhydride, isophthalicacid, terephthalic acid, 1,3,5-trimesic acid, hexahydrophthalic acid.Excess levels of acid over epoxide functionality are used to produce anon-gelled acid functional resin. Generally 0.5 to 2.0 or more moles ofdiacid are used per equivalent of epoxy.

Diaoids or polyaoids are used with the epoxides at an excess equivalentof acid, such that the product is acid functional. For each epoxideequivalent, at least 1,3 and up to 4 or more equivalents of diacid orpolyfunctional acid can be used with a preferred range being between 2and 3 equivalents of di- or poly-carboxylic acid per equivalent ofepoxide. Epoxy-ester molecular weight is increased at the lower acidlevels through chain extension, and excess, untreated diacid remains inthe resin at the higher levels. The excess carboxyl groups on theepoxy-ester provide the curing mechanism for both the zinc activatedionomeric link and the carboxyl-hydroxyl crosslink.

Epoxies will reaot with diaids at 100° to 140° C., without a catalyst,but the reaction proceeds quicker in the presence of a suitablenuoleophile, such as tertiary amine. Good reaction rates in the presenceof about 0.1% benzyldimethyl amine occur at about 80° to 140° C.Processing temperatures above 100° C. allow easier handling of the resinsolution. Solvent stripping can be done under vacuum at 100° to 50° C.Temperatures above 220° C. should be avoided, because resin degradationcan occur. These epoxy-esters can be prepared using reactive extrusiontechniques. In this case, the epoxy resin, diacid, initiator, andnucleophile are premixed, then allowed to reaot under suitabletemperature conditions in extrusion-type equipment. In this procedure,the zinc salts may be added along with pigments, flow modifiers, andother additives to the molten polymer blend, and solvent stripping iseliminated.

Preferred epoxy-esters are prepared from standard bisphenol A typeepoxies and diacids. For powder paints, epoxy and diacid can bedissolved in toluene, heated to 110° C., and then allowed to react inthe presence of about 0.1% tertiary amine. Solvent is stripped off togive a powder resin with a task temperature above 50° C. Resins areblended on a two roll mill or in an extruder with a zinc organic salt,such as zinc propionate or zinc acetate, or zinc carbonate at about 10to 150% neutralization, based on acid content of the resin. The resin isground, sprayed onto parts electrostatically, and then baked undernormal powder coating conditions. Oven temperatures of 350° to 400° F.are suitable.

Referring next to the ionizable organic zinc salt useful for convertingcarboxyl polymers into ionomers, the protonated counterion of the zincsalt characteristically has a pka above about 3.0 and preferably above3.8 at ambient temperatures. The zinc salt organic counterion in itsprotonated form should volatilize in the curing temperature range tocombine the carboxylic acid functional polymer with the zinc salt. It isbelieved that when the acid in the epoxy-ester polymer is substantiallyweaker, the polymer carboxyl group will essentially remain in itsprotonated form. Conversely, when the acid in the copolymer is thestronger acid, its proton will be loosely held and will be readilyavailable to react with the zinc ion. Accordingly, preferred epoxy-esterpolymers require zinc organic salts which have protonated counterionswith an appropriate pka to allow significant ionic interaction with theepoxy-ester carboxylic acid groups and provide crosslinking typepolymeric properties in accordance with this invention. Thus, acidsweaker than, for example, acrylic or methacrylic acid and havingapproximately equivalent or higher pka than these acids provide thedesired ionic interaction between ionic polymer chains to provideionomeric links (ionic crosslink) cured polymer structures. Accordingly,useful zinc organic salts include for example those compounds listed inthe following Table A.

                  TABLE A                                                         ______________________________________                                                                B.P. (°C.) of                                                                     pKa of                                                             Protonated Protonated                                 Salt          M.P. (°C.)                                                                       Counterion Counterion                                 ______________________________________                                        Zn Propionate  185      141         4.87                                      Zn Pentanoate  100      186         4.84                                      Zn Butyrate   >200      163         4.82                                      Zn Hexanoate  >200      206         4.85                                      Zn Stearate    120      358         4.08, 9.85                                Zn Salicylate >200      211         4.06, 9.92                                Zn Pivalate   >200      164         5.03                                      Zn Heptanoate >200      223         4.89                                      Zn Saccharate >200      125         5.00                                      Zn Octanoate   143        239.3     4.90                                      Zn Benzoate   >200      249         4.20                                      Zn Acetate     237      116         4.76                                      Zn Laurate     128      131         4.89                                      Zn Butenoate  >200      185         4.68                                      Zn Ascorbate  >200      190         4.10, 11.80                               Zn Cyclohexylacetate                                                                        >200      243         4.51                                      Zn Decanoate  >200      270         4.95                                      Zn Carbonate  >200      --         10.33                                      ______________________________________                                    

Useful zinc organic salts having the desirable ionic exhibitcharacteristics for carboxylic acid epoxy-ester binders have protonatedcounterions with a pka above about 3.0 and preferably above about 3.8where protonated counterions a boiling point above about 80° C. for usein powder coatings to enable the organic salt to volatilize during theheat curing step or to enable the zinc salt to be soluble in the acidcopolymer.

Useful inorganic zinc salts comprise zinc carbonate which is intended toinclude in-situ formations of zinc arbonate formed when combined withthe carboxylic functional polymer of this invention.

In accordance with this invention, the useful level of neutralization ofthe carbolic acid functional, of neutralization epoxy-ester polymer,based on the equivalent of zinc salt added per equivalent of availablecarboxylic acid funotionality in the copolymer, is above 10% andpreferably between 30% and 150% and most preferably between 50% and 100%neutralization. In this regard, it has been found that excessneutralization of available carboxyl groups on the epoxy-ester does notinterfere with the esterification cure crosslinking reaction occurringduring heat curing. Thus, even though 100% of the available carboxylgroups are neutralized with zinc compounds, the esterificationcrosslinking still occurs to some extent as a competing reaction and isbelieved to dominate in preference to the ionomeric link.

In accordance with this invention, the ionomeric binder is useful inpowder and solvent-borne coatings to provide thermoset-like propertiesto a heat cured paint film. By properly balancing the hydrophobicity andpolarity of the ionomeric polymers of this invention, thermoset,crosslinked-type properties can be achieved upon heating to induce thedesired ionomeric clustering in accordance with this invention. Suitableprocessing temperatures for the ionomer must minimize the amount ofionomeric interactions or clustering during the melt-mixing step of thepowder paint which, ordinary dictates mixing at temperatures slightlyabove the tack temperature of the carboxylic acid polymer but less thanthe volatilization temperature of the acidified counterion of the zincorganic salt or zinc carbonate. Thus, thermal curing of the powder paintcan be readily achieved during the curing cycle without prematuregellation of the powder coating. Resulting paint film integrityproperties resemble crosslinked polymer networks and exhibit high filmhardness as well as considerable resistance to solvent and water. Zincorganic salts useful in powder coatings preferably are solid at ambienttemperatures (25° C.) with a melting point less than the intended curingtemperatures or the salt must be soluble in the acid polymer. Theorganic counterion of the zinc salt in its protonated form preferablyvolatilizes during the intended curing cycle.

Cured paint films produced in accordance with this invention provideionomeric interactions or clustering between ionomer polymer chains in acrosslink-type fashion to produced cured paint films exhibitingconsiderable MEK resistance, water resistance, improved hardness, andother film integrity properties.

The merits of this invention are further illustrated in the followingexamples.

EXAMPLE 1

a. Prepare a resin from:

1600 g GT-7013 epoxy, Ciba-Geigy

584 g adipic acid

1000 g toluene

2.0 g benzyldimethyl amine

Heat the above under nitrogen to 110° C., and stir for 3 hours. Raisethe pot temperature to 140° C., while collecting distilled solvent.Apply a vacuum to remove more solvent. Remove viscous resin from theflask.

b. Preparation of Powder Paint Ionomer Samples

Stoichiometric quantities of copolymer, zinc organic salt, and otheradditives were weighed out and placed into a stainless steel Vita-MixModel 3600 blender. The sample chunks were broken by pulsing theVita-Mix until the larger pieces were crushed. The samples werepulverized by grinding at high speed for 15 seconds in the forward modeand 15 seconds in the reverse mode. The powdered material was placed inpolyethylene bags.

The powdered pre-mixed samples were melt-mixed using a Brabender tworoll, water cooled mill. The mill was set to the appropriate meltingtemperature of the materials to be mixed and turned on in the forwardmode. The powdered samples were sprinkled slowly over the hot roll andallowed to melt and mix by adjusting the spacing at the nip. When theentire sample was on the mill, the speed was adjusted to the highestsetting. The sample was mixed for three minutes, with scraping andremixing every one minute. The molten sheet of resin was scraped fromthe mill and cooled to room temperature. The melt-mixed samples werebroken into flakes by using a rubber mallet or the Vita-Mix blender.These flakes were fed into a Brinkman or Tecator grinder using avibratory bed and a 0.5 micron screen at low speed. When the entiresample was ground, it was removed from the grinder and was sievedthrough a 120 mesh brass or stainless steel screen using a sieve shaker.

c. Panel Preparation

The prepared powder paint samples were collected and electrostaticallysprayed over cold rolled steel at a film thickness of approximately 1.5to 2.0 mils. The steel panels were baked at an appropriate bakingtemperature, cooled and evaluated for film performance.

d. Test Samples.

Combine 100 g of the above with stoichiometric quantities of anappropriate zinc salt such as zinc propionate, blend the dry ingredientstogether in a standard laboratory high speed blender, and melt mix thepowder on a Brabender two roll mill at a hot roll temperature of 120 C.(See Table I). Cool and pulverize the product in a Telator grinder.Apply the lear powder coating to Parker Chemical Bonderite-1000 panelsat 1-2 mils. Bake for 20 minutes at 400° F. in a gas fired oven.

EXAMPLE 2

2. Prepare as in Ex. 1, but use 752 g. azelaic in place of the adipicacid. See Table I.

EXAMPLE 3

3 Prepare as in Ex. 1, but use 920 g. dodecanedioic acid in place of theadipic. See Table I.

                                      TABLE 1                                     __________________________________________________________________________    Epoxy-Ester Ionomeric Powder Coatings Examples 4 Through 12                             Zn salt                                                                             g salt/              Reverse                                                                            Direct                                   Diacid                                                                             (100% 100 g                                                                              Melt Proc.                                                                           Pencil                                                                             MEK*                                                                              Impact                                                                             Impact                                                                             Conical                        Example                                                                            Used Neut.)                                                                              polymer                                                                            Temp. (°C.)                                                                   Hardness                                                                           Rubs                                                                              (In.-lbs.)                                                                         (In.-lbs.)                                                                         Mandrel                        __________________________________________________________________________    4    Adipic                                                                             None  0    120    H     50 160  160  Pass                           5    Adipic                                                                             Propionate                                                                          19.36                                                                              120    2H   100 160  160  Pass                           6    Adipic                                                                             Carbonate                                                                           11.48                                                                              120    5H-6H                                                                              100 160  160  Pass                           7    Azelaic                                                                            None  0    80     HB    80 160  160  Pass                           8    Azelaic                                                                            propionate                                                                          17.96                                                                              80     4H   100 160  160  Pass                           9    Azelaic                                                                            Carbonate                                                                           10.64                                                                              80     H    100 160  160  Pass                           10   DDA  None  0    90     2B    20  5    30  Cracks                         11   DDA  Propionate                                                                          16.80                                                                              90     2H   100 160  160  Pass                           12   DDA  Carbonate                                                                           9.96 90     H    100  20   40  Cracks                         __________________________________________________________________________     *Number of double rubs until breakthrough to substrate.                  

SOLUTION EPOXY-ESTERS

Epoxy-esters were prepared by reacting adipic acid or azelaic acid ordodecanedioic acid with epoxy resin in xylene as described in Examples1-3. A 10% solution of zinc propionate in DMSO was added to each polymerto provide 100% neutralization based on equivalent weight. Films weredrawn down over Bonderite 1000 (Parker Chemioal) using a 0.006 inch Birdblade. The films were baked at 400°F. for 20 minutes and the resultingpoured film properties are shown in Table II.

                  TABLE II                                                        ______________________________________                                        Property     DDA        Adipic  Azelaic                                       ______________________________________                                        Pencil Hardness                                                               Unneutralized                                                                              2B         H       HB                                            Neut. (ZnProp)                                                                             2H         2H      4H                                            MEK Resistance*                                                               Unneutralized                                                                                30         65    >100                                          Neut. (ZnProp)                                                                             >100       >100    >100                                          Impact (in lbs.)                                                              Direct                                                                        Unneutralized                                                                               <30       >160    >160                                          Neut. (ZnProp)                                                                             >160       >160    >160                                          Reverse                                                                       Unneutralized                                                                               <5        >160    >160                                          Neut. (ZnProp)                                                                             >160       >160    >160                                          60# Gloss (%)                                                                 Unneutralized                                                                              93.4       76.5    72.5                                          Neut. (ZnProp)                                                                             14.0       36.8    14.7                                          ______________________________________                                         *Number of double rubs until break through to substrate.                 

EXAMPLE 14

Epoxy-ester Powders

Epoxy-esters described in Examples 1, 2, and 3 were evaluated as powdercoatings using zinc propionate neutralization at 0 and 100 % based onequivalent weight. Coatings were applied eleotrostatically to Bonderite1000 (Parker Chemical) panels and baked for 20 minutes at 400° F.

Coating properties are illustrated in attached Table III.

                                      TABLE III                                   __________________________________________________________________________    Property     DDA     Adipic  Azelaic                                          __________________________________________________________________________    Neut.          0  100                                                                                0  100                                                                                0  100                                         Film Build (mils)                                                                           2.35                                                                              2.25                                                                              2.50                                                                              2.15                                                                              2.60                                                                              2.55                                        Pencil Hardness                                                                            2B  2H  H   2H  HB  4H                                           MEK Resistance*                                                                             30 >100                                                                                40                                                                              >100                                                                              >100                                                                              >100                                         Impact (inch-lbs.)                                                            Rev.          <5 >160                                                                              >160                                                                              >160                                                                              >160                                                                              >160                                         Direct       <30 >160                                                                              >160                                                                              >160                                                                              >160                                                                              >160                                         Viscosity (175° C.) (Poise)                                            Time = 60"   8.0 78.0                                                                              55.0                                                                              45.0                                                                              17.0                                                                              22.0                                         Time = 180"  9.0 84.0                                                                              61.0                                                                              Gel 17.0                                                                              27.0                                         __________________________________________________________________________     *Double rubs until breakthrough to substrate.                            

EXAMPLE 15

The epoxy-ester polymer as described in Example 1 was evaluated as apowder coating at various levels of neutralization by combination withzinc carbonate. Materials were melt mixed on a Brabender two roll mill,ground using a Tecator grinder, and sieved through a 140 mesh screen.These coatings were electrostatically sprayed over Bonderite 1000(Parker Chemical) and baked for 20 minutes at 400°F. Coating propertiesare shown below. These results illustrate the esterification cure asacceptable coating properties are obtainable without zincneutralization.

    ______________________________________                                        % Neut.      0       21.0    42.1  63.2  54.2                                 MEK Resistance*                                                                            >100    >100    >100  >100  >100                                 Pencil Hardness                                                                            2H      6H      6H    6H    6H                                   Impact (inch-lbs.)                                                            Direct       >150    >160    >160  >160  >160                                 Reverse      >150    >160    >160  >160  >160                                 Gel Time (sec.)                                                                             300     240     182   120    60                                 MEK Dissolution                                                                            11.66   1.55    1.30  0.74  1.28                                 (% Weight loss)                                                               Viscosity (175° C.)                                                                 140 p   179 p   214 p 273 p 364 p                                (345 sec)                                                                     ______________________________________                                         *Double rubs until breakthrough to substrate.                            

These drive coatings were evaluated for Tg using differential scanningcolorimetry (DSC). If ionomer formation is occuring, one would expect ashift in Tg or the appearance of a second Tg characteristic of theionomeric phase.

Results show Tg increase with neutralization.

    ______________________________________                                               % Neut.                                                                              DSC Tg                                                          ______________________________________                                               0      35° C.                                                          21.0   39° C.                                                          42.1   45° C.                                                          63.2   54° C.                                                          84.2   60° C.                                                   ______________________________________                                    

EXAMPLE 16

Two polymers prepared as in Example 1 were evaluated as powder coatingsneutralized with zinc carbonate.

    __________________________________________________________________________               Polymer A    Polymer B                                             __________________________________________________________________________    % Neut.    0    42.1                                                                              84.2                                                                              0    42.1                                                                              84.2                                         60° Gloss (%)                                                                     66.1 92.9                                                                              46.3                                                                              77.4 71.8                                                                              65.4                                         Impact (inch-lbs.)                                                            Direct     >30  >160                                                                              >160                                                                              >50  >160                                                                              >160                                         Reverse    >10  >160                                                                              >160                                                                              >70  >160                                                                              >160                                         Conical    fail pass                                                                              pass                                                                              fail pass                                                                              pass                                         Mandrel    (40 mm)      (65 mm)                                               MEK        >100 >100                                                                              >100                                                                              >100 >100                                                                              >100                                         Resistance                                                                    (Double rubs until                                                            breakthrough to                                                               substrate).                                                                   Viscosity  310 p                                                                              391 p                                                                             404 p                                                                             312 p                                                                              399 p                                                                             499 p                                        (Poise, 75° C., 225 sec)                                               __________________________________________________________________________

EXAMPLE 17

A polymer was prepared as in Example 1 and tested for coating properties(as described in earlier methodology). Resiflow PL200 (Estron Chemical,Inc.) and benzoin were added to the polymer/salt blend to aid in flowand leveling. Results shown below support dual cure esterification andionomer formation.

    ______________________________________                                        % Neut.      0       25      50    75    100                                  60° Gloss (%)                                                                       91.2    81.3    96.1  94.6  96.5                                 Pencil Hard. 3H      6H      8H    6H    6H                                   Knoop Hard.  14.16   13.80   13.60 13.58 13.70                                MEK Resist.  >200    >200    >200  >200  >200                                 (Double rubs until                                                            breakthrough to                                                               substrate)                                                                    Impact (in lbs.)                                                              Direct       30      100     >160  >160  >160                                 Reverse      60      120     >160  >160  >160                                 Viscosity @ 175° C.                                                    poise                                                                         (240 sec)    185     183     239   223   257                                  Weatherometer                                                                 Exposure                                                                      Total Color Change                                                             660 hrs     0.97    0.66    1.07  0.89  1.77                                 1491 hrs     1.46    1.76    1.65  1.31  2.73                                 ______________________________________                                    

EXAMPLE 18

A polymer was prepared in Example 1 and formulated into a pigmentedpowder coating at a 0.06 P:B using TiO₂, Resiflow PL200, (EstronChemical, Inc.) benzoin, and ZnCO₃, The powder coating was melt mixed ina Brabender two Roll Mill, ground, and sieved. It was electrostaticallysprayed onto Parker Conderite 1000 cold rolled steel and baked for 20400° F.

    ______________________________________                                        Coating Properties:                                                                            Unneutralized                                                                              Neutralized                                     ______________________________________                                        MEK Resistance    75          >250                                            (Double rubs until                                                            breakthrough to substrate)                                                    Impact (inch-lbs.)                                                            Direct           <40          >160                                            Reverse          <20          >160                                            Conical Mandrel  Pass         pass                                            Hardness                                                                      Pencil           3H           6H                                              Knoop (KHN)      18.49        21.53                                           ______________________________________                                    

We claim:
 1. In a process for producing a heat cured thermosettingprotective coating composition containing a reactive polymeric binder,the process steps comprising:producing a reactive polymer binder systemcomprising a carboxyl functional polymer have an Acid No. above 10 andnumber average molecular weight between about 500 and 100,000 where thecarboxyl functional polymer is an epoxy-ester copolymer is the reactionproduct of an epoxy resin with excess equivalents of dicarboxylic acidcomprising from 1.3 to 4 equivalents of carboxylic acid per equivalentof epoxide, said epoxy-ester copolymer having both carboxyl groups andhydroxyl groups; intermixing the epoxy ester copolymer with a zinc saltselected from the zinc carbonate, or an organic zinc salt having a pkaabove about 3.8 and in sufficient amounts to neutralize at least 10% ofthe equivalents of carboxyl groups of the carboxyl polymer; and heatcuring said coating composition through a dual curing mechanism wherethe zinc salt coreacts with the neutralized carboxyl groups while theremaining carboxyl groups coreact with said hydroxyl groups to form athermoset coating film.
 2. The process in claim 1 where the zinc salt iszinc carbonate.
 3. The process in claim 1 where the zinc salt is anorganic zinc salt.
 4. The process of claim 1 where the zinc saltneutralized at least about 30% of the equivalents of carboxyfunctionality of the carboxyl polymer.
 5. The process of claim 1 wherethe epoxy-ester is produced in an extrusion process where said epoxyresin and said dicarboxylic acid are intermixed in an extruder and underheat coreacted to from said epoxy-ester copolymer.
 6. the process inclaim 1 where the coating composition is applied as a coating film tothe surface of a substrate; andthe applied coating film is heated to aheat curing temperature above about 120° C. to coreact the zinc saltwith the carboxyl functional polymer.
 7. The process in claim 6 wherethe applied coating is heat cured at temperatures between about 150° C.and 200° C.